GENEVA  Damage from the Indian Ocean tsunami could have been reduced if more coastal areas had maintained their protective shields of mangrove swamps and coral reefs, a key U.N. official said Friday.

Pasi Rinne, who is heading the U.N. Environment Program's response to the disaster, agreed with conservation groups that the swamps and reefs not already destroyed by humans may have reduced some of the damage caused by the tsunami.

Mangroves grow in thickets along tropical coastlines and their complicated root systems help to bind the shore together, effectively providing a shield against destructive waves.

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"These act as shock absorbers for the types of flooding and the tsunami that we saw," said Simon Cripps, head of the Worldwide Fund for Nature's marine program based in Gland, Switzerland.

"It wouldn't have been able to stop it completely, of course, but we've seen areas already ... where there were mangroves, there was substantially less damage."

Rinne said, however, that it still has to be confirmed whether mangroves and coral reefs prevented significant damage from the Indian Ocean tsunami.

"It's not only an early warning system that is going to help, we also have to look how we construct, how we use the coastal zones," he said.

Many lives could have been saved if mangroves and reefs had been conserved in a healthy state, said the Mangrove Action Program, an environmental organization based in Port Angeles, Washington.

"Instead these vital protective buffers that nature provides against wind and wave had been foolishly degraded or removed for unsustainable developments," the organization said in a statement.

An official of the 144-nation Ramsar treaty protecting the world's wetlands said initial assessments indicated mangroves had lessened some of the impact of the tsunami.

"Mangroves are recognized as being one of the coastal systems that provides buffering against storms and storm effects from the sea," said Nick Davidson, deputy chief of the secretariat for the Ramsar Convention on Wetlands, which also is based in Gland, near Geneva.

But, he said, it remains unclear whether mangroves and coral reefs had a significant protective effect against a "tsunami on the scale that we've just witnessed."

Up to half of the world's mangrove swamps have disappeared in the last 20-30 years because of the development of tourist resorts, transport infrastructure and commercial prawn fishing, Cripps said in a telephone interview.

The Mangrove Action Program estimates that there are 16,000 hectares (40,000 acres) of mangroves left in the world.

This makes coastal areas more susceptible to flooding, as has previously been seen in Bangladesh, which no longer has a protective shield of mangroves.

"The advantage of mangroves is severalfold," Cripps said. "They hold the structure of the land together, the coastline together."

Coral reefs have been similarly hit by waste water from new developments, dynamite fishing and warmer water because of climate change.

An offshore coral reef also seems to have prevented much more widespread destruction on the low-lying Maldives islands, Cripps noted.

Cripps cited the example of the Marriott hotel in Phuket, Thailand, which was built next to a turtle nesting beach and so was developed with strict environmental guidelines. The hotel was built back from the beach and development of the waterfront was severely restricted, so mangrove swamps were preserved along the coast.

"Apparently the damage, the actual physical damage, and the human loss of life was very much less than in other areas and other hotels in the region," he said.